The 1.7Aa resolution structure of At2g44920, a pentapeptide-repeat protein in the thylakoid lumen of Arabidopsis thaliana

• Published in: Acta crystallographica. Section F, Structural biology and crystallization communications Structural biology and crystallization communications, 2011-12, Vol.67 (12), p.1480-1484
• Main Authors: Ni, Shuisong, McGookey, Michael E, Tinch, Stuart L, Jones, Alisha N, Jayaraman, Seetharaman, Tong, Liang, Kennedy, Michael A
• Format: Article
• Language: English
• Subjects: Amino acids; Crystal structure; Cyanobacteria; Genes; Genomes; Lumens; Position (location); Proteins
• ISSN: 1744-3091; 1744-3091
• DOI: 10.1107/S1744309111037432

At2g44920 belongs to a diverse family (Pfam PF00805) of pentapeptide-repeat proteins (PRPs) that are present in all known organisms except yeast. PRPs contain at least eight tandem-repeating sequences of five amino acids with an approximate consensus sequence (STAV)(D/N)(L/F)(S/T/R)(X). Recent crystal structures show that PRPs adopt a highly regular four-sided right-handed beta -helical structure consisting mainly of type II and type IV beta -turns, sometimes referred to as a repeated five-residue (or Rfr) fold. Among sequenced genomes, PRP genes are most abundant in cyanobacteria, leading to speculation that PRPs play an important role in the unique lifestyle of photosynthetic cyanobacteria. Despite the recent structural characterization of several cyanobacterial PRPs, most of their functions remain unknown. Plants, whose chloroplasts are of cyanobacterial origin, have only four PRP genes in their genomes. At2g44920 is one of three PRPs located in the thylakoid lumen. Here, the crystal structure of a double methionine mutant of residues 81-224 of At2g44920, the naturally processed fragment of one of its full-length isoforms, is reported at 1.7Aa resolution. The structure of At2g44920 consists of the characteristic Rfr fold with five uninterrupted coils made up of 25 pentapeptide repeats and alpha -helical elements capping both termini. A disulfide bridge links the two alpha -helices with a conserved loop between the helical elements at its C-terminus. This structure represents the first structure of a PRP protein whose subcellular location has been experimentally confirmed to be the thylakoid lumen in a plant species.